Nigerian officials Wednesday said four people were killed as 721 prisoners escaped from a federal prison in Bauchi, northeastern Nigeria, the previous evening.
Danlami Yar'adua, Bauchi state police commissioner, disclosed that a soldier, a policeman and two civilians were killed during the violent prison break, which was believed to have been staged by a militant Islamist group.
Yar'adua said six others, including three prison wardens, are critically ill in hospital.
The prison held 186 members of Islamist sect Boko Haram - the name translates as "Western education is a sin". The prisoners have been awaiting trial since violent clashes in July 2009.
The group stormed the prison in large numbers and began shooting to gain entry. They moved from cell to cell to free the prisoners before setting fire to a section of the facility.
Boko Haram, founded in 2002 in the northeastern city of Maiduguri by Ustaz Mohammed Yusuf, attacked police stations and private homes in several clashes in Bauchi last year. Over 700 people died in the violence.
Officials said that Bauchi is now calm after the escape.